Smart skin array woven fiber optic ribbon and arrays and packaging thereof

ABSTRACT

A woven material is described in which optical fibers are positioned and held in the material in a manner to maximize their optical efficiency. The material consists of fibers extending in both the warp and woof direction, the optical fibers are positioned in channels between the supporting fibers in the warp direction. The material is manufactured using conventional weaving equipment by positioning both the optical fibers and the warp fibers, and then weaving the woof fibers into place without bending the optical fibers. The fibers are thusly woven so that the optical fibers have zero warp. The woven grid-like mat can be coated with a protective material that either enables it to form a flexible sheet of ribbon or a rigid, hard, grid-like mat which has aligned zero warp optical fibers embedded therein. The material shown can be used to provide sensing, imaging or communications. It can be utilized for optical backplanes for optoelectronic systems or a housing for optoelectronic components.

This is a Division of application Ser. No. 07/998,234, filed Dec. 30,1992, now abandoned, which is a Division of application Ser. No.07/671,582 filed Mar. 19, 1991, now U.S. Pat. No. 5,256,468.

BACKGROUND OF THE INVENTION

This invention relates to optical systems and optical fibers, andparticularly to optical fibers woven into other material to providesensors or "smart" skins for aircraft and other applications.

Fiber optic sensor technology has become increasingly desirable formonitoring for numerous applications such as aircraft and spacecraft.The size, weight, communications density, immunity to interference, andruggedness, are pushing fiber optic technology into more and moreapplications.

A recent concept in the manufacture of aircraft and spacecraft has beenthe employment of fiber optics within the skin of the craft itself,thereby creating a "smart" skin which enables sensors embedded into thecomposite material to convey information about the aircraft orspacecraft throughout the craft without need for separate communicationslinks and their associated disadvantages.

The mechanical properties of cloth woven from glass fibers arereasonably well known. Such material provides desirable mechanicalproperties including high tensile strength, flexibility, resistance toweather as well as chemicals, high tear strength, dimensional stability,and abrasion resistance.

It is also known that individual optical fibers can be used to transmitoptical signals throughout the length of the fiber and have very highbandwidths. Individual optical fibers have excellent optical properties,but are very fragile. A variety of techniques have been developed tohold individual fibers in a manner to prevent damage to them. Forexample, they are frequently encased in cables or other protectivematerial. In addition, individual fibers can be grouped together toprovide cables capable of carrying increased amounts of information.

One technique widely used for protection of optical fibers is toencapsulate them in an epoxy material to provide rigidity and strength.For example, U.S. Pat. No. 4,547,040 describes an optical fiber assemblywhere optical fibers are held in an embedding material.

Individual optical fibers have also been woven into sheets. For example,U.S. Pat. No. 4,907,132 describes a device where optical fibers arewoven into a panel. The fibers are positioned in the warp direction ofthe weave. Where the fibers cross the woof fibers, the coating isremoved so that the fibers emit light. In this manner, a panel made fromthe fibers emits light. U.S. Pat. No. 4,885,663 shows woven opticalfibers where the bends in the fibers where they cross the woof providediscontinuities for the emission of light. The purpose of this structureis provide a light-emitting panel.

Other prior art such as U.S. Pat. Nos. 4,952,020 and 4,468,089 showoptical fibers which are encapsulated in various ways to form cableassemblies such as described above. Unfortunately, cable assemblies suchas described in these patents are relatively expensive and cannot beused to form sheet-like structures.

Many papers have been written on the application of optical fibers tothe formation of "smart" skins for aircraft or spacecraft. In "FiberOptic Skin and Structural Sensors," by Eric Udd, Industrial Metrology 1(1990) 3-18, the use of optical fibers in a skin-like material for useas sensors is described. The paper, however, describes the fibers asbeing merely embedded in a structural material. Embedding the fibers inthat manner suffers from the disadvantages discussed in the paperdiscussed below.

In a paper entitled, "Smart Skins and Fiber-optic Sensors Applicationand Issues," Kausar Talat, Boeing Defense & Space Group, Seattle, Wash.(unpublished), describes material with embedded optical fibers where thephysical properties of the fiber itself were used as a sensor. Thecomposite described in this article includes optical fibers disposedinside a laminated structure. At the end of the structure, the opticalfibers pass through a tube inserted to prevent micro-bending of thefiber where it exists from between the laminated sheets. As described inthe article, the laminated structure causes the fibers to kink duringcuring, creating losses as well as having other disadvantages discussedin the paper.

SUMMARY OF THE INVENTION

The present invention provides a structure which solves many of thealignment problems present in the above-described prior art. Accordingto the technique of this invention, the optical fibers are woven into asupporting material in channels therein. The optical fibers arepositioned to have zero warp and be without cross-overs or micro-bends.

According to the present invention, optical fibers are positioned andheld in a grid-like mat woven from fibers of a supporting material. Thissupporting material can consist of any desired material providing therequisite properties, for example, fiberglass, graphite, etc. Thesupporting fibers are used for both the warp and woof fibers for thestructure. During manufacture, one or more optical fibers are positionedin channels between the supporting fibers in the warp direction. Eachchannel can have a large number of optical fibers.

The material is woven so that the optical fibers have zero warp, thatis, they have no bends. This enables the optical fibers to operate withmaximum transmission efficiency. Once complete, the woven grid-like matcan be coated with protective material such as rubber epoxy to form aflexible sheet with zero warp optical fibers embedded within it.Alternatively, the material can be coated or embedded in a rigidmaterial, such as epoxy, to form a hard or rigid grid-like material.

The material fabricated according to this invention has manyapplications and can be used to provide sensing, imaging, andcommunications. For example, the material is suitable for communicationof sensing information on the surface of an aircraft or spacecraft.

In a preferred embodiment of the invention, the woven structure includesa plurality of first strands positioned in a warp direction and aplurality of second strands positioned in a woof direction, the secondstrands being woven with the first strands. The optical fibers arepositioned in the structure between selected pairs of the first strandsin a manner such that the optical fibers have zero warp.

In another embodiment of the invention, an optoelectronic packagingstructure includes two portions. In both portions a plurality of firststrands are positioned in a warp direction and a plurality of secondstrands are positioned in a woof direction, interwoven with the firststrands. In only a first portion of the structure, however, are aplurality of optical fibers woven into the structure in a manner suchthat they have zero warp and extend in channels defined by the firststrands. The optical fibers extend from the first portion of thestructure and connect to components affixed to the second portion of thestructure, and/or to other structures in or out of the plane of theoriginal weave.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of material having both woven support fibers andoptical fibers;

FIG. 2 is a cross-sectional view of the material shown in FIG. 1;

FIG. 3 illustrates a larger section of woven material and termination oftwo edges of material;

FIG. 4 illustrates another embodiment of the invention in which aparallel weave of separable optical fiber ribbons of one type are wovenwith other material and can be separated into individual ribbons;

FIG. 5 illustrates another embodiment of the invention showing fiberoptic ribbons having a plurality of two fiber optic strands per ribbon;

FIG. 6 illustrates a three-dimensional packaging structure; and

FIG. 7 illustrates another application of the invention in which theoptical fibers extend beyond the material to permit easierinterconnection.

DESCRIPTION OF THE SPECIFIC EMBODIMENT

FIG. 1 is a plan view of a preferred embodiment of material fabricatedaccording to the invention. As illustrated, the material is woven withwarp strands 10A, 10B, 10C, 10D, and woof (or pick) strands 11A, 11B,11C and 11D. The warp and woof strands are woven together into afabric-like material using a normal over-and-under plain weave pattern.The warp and woof strands may employ any desired material having thephysical properties desired for the application. For example, thestrands can comprise fiberglass, graphite, silica carbide, or othermaterials. An example of a silica carbide fiber suitable for applicationis sold by Dow-Corning Corporation under the trademark NICALON™.

Introduced with the supporting fibers before the weaving are opticalfibers 12A, 12B, 12C, 12D, 12E and 12F. Importantly, the optical fibersare introduced into the material to run in the warp direction with azero warp. That is, the optical fibers have no bending or crimping. Theabsence of bends or crimps provides maximum optical efficiency andprovides repeatability of signals regardless of their transmissionposition within the woven material. It is well known that when signalsare transmitted through optical fibers, losses occur wherever bending orkinking of the fiber is present. The structure shown in FIG. 1 includesa pair of optical fibers in the channel between each non-optical warpstrand 10A, . . . 10D. Of course, more or fewer optical fibers may beemployed.

FIG. 2 is a cross-sectional view of material such as depicted in FIG. 1,but which has also been coated with a protective coating material tohold all fibers in place. FIG. 2 can be considered to be across-sectional view of the structure shown in FIG. 1 taken along thelength of fiber 12A. As shown in FIG. 2, the optical fiber 12A extendsacross the figure with woof strands 11A, 11B, 11C and 11D extending overand under the optical fiber. A coating 20 consisting of a well knownmaterial such as rubber, epoxy, or other suitable material, holds theoptical fibers in position with respect to the surrounding material.

FIG. 3 depicts a larger region of material woven according to thepreferred embodiment to illustrate the manner in which the woof strandsare bound at the edges of the material. As shown in FIG. 3, the opticalfibers 12 extend from the top of the figure to the bottom, while thewoof strands extend across the figure from left to right. Also extendingfrom the top of the figure to the bottom are the warp strands discussedabove in conjunction with FIG. 1. The edges of the woof strands 11 arebound by a conventional technique using leno material 31 and 32. 0fcourse, other techniques may also be employed to secure the edges of thefabric, for example by knotting them together.

For the embodiment depicted in FIG. 3, silica carbide fibers such asthose described above are employed which have a dimension of 1800 denierand are woven with a density of 44 optical fibers per inch. The densityof the weave is defined both by the diameter of the optical fiber, thesurrounding material and the width of the teeth of the comb, and isvariable as necessary depending upon the application.

The optical fibers embodied in the fabric depicted in FIG. 3 arecommercially-available optical fibers such as graded index GE-dopedsilica fibers manufactured by Corning or single mode silica fibers, etc.In one embodiment Corning fibers with an numerical aperture of 0.22, acore of 125 microns with an overall diameter of 250 microns and an 85°C. temperature rating are employed. Using fibers such as these in amaterial as described results in about 44 fibers per lineal inch acrossthe material. The length of the material is dependent on the length ofthe roll of material used, and very long rolls of material, exceeding akilometer in length, can be fabricated using existingcommercially-available weaving equipment with adequate tension controlmethods applied. The optical fibers can be positioned, and thesurrounding material woven, using conventional textile weavingequipment. For example, a composite generation facility with standardweaving equipment can be employed. Preferably, a comb will be employedin addition to the standard weaving equipment to position the opticalfibers. The comb can be in the form of a small-toothed comb installed atthe front end of the weaving equipment. Such a comb provides areproducible number of fiber optic strands between the strands of theintervening material and assures a nonoverlapping condition with unbentoptical fiber. Although various commercial machines will requiredifferent adjustments, during one test of the weaving operation, achange in tension occurred when the weaving spinner rollers ran out offiber. This change in tension can cause breakage of the optical fiber,and accordingly the importance of controlling proper tension by suitablemonitoring and maintenance of full rollers is believed to be important.In the prior art and presently, optical fibers were laid out manually incomposite plies in specific orientation. Misalignment of the opticalfiber orientation results in significant losses. In the techniquesdescribed herein, the laying out of the fiber is achieved automaticallyin the normal weaving process. Reducing such losses provides for auniformity and repeatability that lends itself to accurate and diversemodality sensing and simple interconnect processes. One of the mostimportant issues is sensor network integration within the structure.This invention successfully addresses this issue as it relates to majorsystems.

For the embodiment depicted in FIG. 3, two optical fiber yarns areplaced in the channel between each of the warp strands. It should beunderstood, however, that any desired number of optical fibers can beplaced between each of the warp strands. For example, in one embodimenteach channel contains eight optical fibers. Other embodiments arediscussed below.

Once the material has been woven with the optical fibers in position,the assembly may be coated with a desired material to give addedprotection to the structure. As described in conjunction with FIG. 2, byapplying a coating to the woven grid-like mat, the position of thefibers in the plane of the grid-like mat is fixed, and the material isprovided with additional rigidity. Preferably, the curing material canbe applied by brushing it onto the woven sheet, by passing the wovensheet through a bath of curing material, or by employing otherconventional application techniques.

In one embodiment of the invention, the rigid coating was made using acuring fluid made from the EPON 828 epoxy, manufactured by ShellChemical Company, mixed with a fixing agent of diethylene-triamine in aratio of 88% epoxy and 12% fixing agent by volume. In other embodimentswhere a flexible material is desired, commercial grade rubber cement hasbeen employed.

FIG. 4 illustrates another embodiment of the invention as ribbons ofmaterial. As shown there, the material is divided into two sections, 51and 53. These sections are separated by additional longitudinal lenofilaments 54 and 55, and an extra support fiber 57. The leno filaments54 and 55 provide a convenient place where the optic grid can beseparated into individual ribbons, provide a convenient marker foridentifying particular fibers, as well as preventing the material fromunraveling. Of course, any desired number of sections can be used in thematerial. In this manner, a large loom can be used to weave in parallelwidths of like or varied materials later divided into sections forvarious uses.

FIG. 5 depicts another embodiment of the invention in which eightoptical fibers 61, 62, . . . 68 are positioned in pairs between twosupport fibers. Lenos 64 with associated extra support fibers 75 and 76are provided to enable one strip of material to be fabricated with anumber of sections and then divided into separate pieces if desired.

FIG. 6 illustrates a three-dimensional woven structure suitable forvarious packaging considerations. As shown, the structure includes awoven backplane 40 with fiber optic conductors 42 and two woven planes44 approximately perpendicular to the backplane. This structure can beused to support printed circuit boards and/or wafers which interface tothe fiber optics in the backplane. This section could be at variousangles relative to the backplane. It is suggested that sharp angles beavoided. All sections moving out of the plane should be rounded at anangle no less than the specified radius in the optical fiber datasheets. This avoids undue stress at sharp edges of the supportingmaterial. Coatings applied to the material can supply additional stressrelief.

FIG. 7 is a perspective view illustrating how the material shown inFIGS. 1, 2 and 3 may be fabricated into a three-dimensional structure.For the structure depicted in FIG. 7, the optical fibers 12 extendbeyond one edge of the woven material to facilitate optical connections.As also shown in FIG. 7, the warp fibers 10 are woven through thematerial in a continuous fashion. By extending the material beyond thearea where the optical fibers are woven into the mat, an additional areaof supporting material provides a structure for mounting othercomponents 15. Of course, components 15 may also be mounted proximate tothe optical fibers to enable connections at that location as well.Components 15 will typically comprise electronic, optical orelectrooptical components. As one example, an optical detectorintegrated circuit can be mounted on the woven cloth mat, andappropriate connections made to surrounding integrated circuits usingwire bonding, flexible printed circuit connections, or other well knowntechniques. Of course, circuits can be mounted on either or both sidesof the material.

Before or after mounting the circuits, depending upon the particularapplication, the structure shown in FIG. 7 can be coated with anappropriate material to hold it in a rigid position or to allow it toflex.

As shown in FIG. 7, the material of this invention provides a structurewhich facilitates various packaging techniques for circuits. With thestructure depicted, the optical fibers are held in a precise locationfacilitating connection to other integrated circuits or other opticalelements. Similarly, by extending the woven material beyond the circuitsubstrate portion, a convenient, inexpensive, integrated technique formounting circuit elements for connection to the optical fibers isprovided. Of course, sensors may be connected to individual fibers orgroups of fibers to provide large arrays of sensors. In addition, theoptical fibers themselves can be used as sensing elements to provide asmart skin array. Examples of such applications of "smart" skin arraysare described in the two technical papers referred to above. The "smart"skin can provide fiber optic sensing arrays in the skin of airplanes. Itcan be used to fabricate low cost, high speed communications forcomputer networks. For example, the material can be employed as anoptoelectronic backplane for large scale, high performance computersystems, such as parallel processors.

The material of the invention also provides a structure for transmissionand reception of laser-generated optical signals in conjunction withpackaging and interconnecting components. Such embodiments can be usedto provide high speed data buses to interconnect components in a highperformance computer system. Of course, the use of large numbers ofoptical fibers provides an ease in constructing systems whereinredundant means for transmission of information is desired as well asfor multichannel information transfers.

Although the foregoing invention has been shown and described withrespect to preferred embodiments, it will be understood that manyalternative embodiments can employ the techniques described here.Accordingly, the scope of the invention is set forth by the followingclaims.

I claim:
 1. A method of fabricating a woven structure containing opticalfibers, comprising:positioning first strands of a first material in awarp direction, the first strands forming channels between adjacentstrands; positioning optical fibers in the warp direction in thechannels formed by the first strands, the optical fibers beingpositioned in zero warp and having diameters less than the firststrands; and weaving second strands of a second material around thefirst strands thereby forming the woven structure in which the opticalfibers are supported; wherein the optical fibers are supportedsubstantially straight and parallel by the woven structure so as tofacilitate transmission of light through the optical fibers.
 2. A methodof fabricating a woven structure as in claim 1 wherein the wovenstructure has an upper and a lower surface, and furthercomprising:coating encapsulation material over both the upper and lowersurfaces to secure the first and second strands and the optical fibersin place.
 3. A method as in claim 2 wherein the encapsulation materialcreates a rigid structure.
 4. A method as in claim 3 wherein theencapsulation material comprises an epoxy.
 5. A method as in claim 2wherein the encapsulation material forms a flexible structure.
 6. Amethod as in claim 5 wherein the encapsulation material comprisesrubberized cement.
 7. A method as in claim 1 wherein at least one of thefirst and second materials comprises a material chosen from the group offiber glass, graphite and silica carbide.